1. Field of the Invention
The present invention is directed to extracorporeal lithotripsy devices, and in particular to such devices making use of a shock wave source applied against the body of a patient.
2. Description of the Prior Art
It is known to use a source of shock waves, applied against the body of a patient, to cause focused shock waves to converge within a zone at wich a calculus, such as a kidney stone or a gall stone, is located. The calculus disintegrates into fragments by the action of the shock waves, and the fragments can be eliminated (excreted) naturally, or can be completely or partially dissolved using chemotherapeutic measures (litholysis).
An apparatus of this type is described in U.S. Pat. No. 4,674,505 which includes a shock wave source which generates shock waves converging in a focus zone lying on the acoustic axis of the shock wave source. The apparatus also includes a generator and a control circuit for driving the shock wave source. The shock wave source includes means for acoustically coupling the source to the body of the patient into whom the shock wave are to be introduced, and for adjusting the apparatus and body of the patient relative to each other.
This apparatus achieves good results in the treatment of kidney stones without having recourse to additional chemotherapeutic measures. It is nonetheless desired to increase the effectiveness of this known apparatus. In this context, an increased effectiveness means a reduction in the required number of shock waves to treat a calculus with a simultaneously increase in the degree of disintegration. Such an increased effectiveness results in a shortened treatment time and simultaneously assures that the calculus (or calculi) will be disintegrated into smaller fragment which can be more easily eliminated or, if necessary, can be more quickly dissolved with chemotherapeutic measures, because the surface area to volume ratio becomes larger as the fragments become smaller. Such an increased effectiveness thus means that the stress on the patient from the treatment is lower because not only is the dose of acoustic energy diminished (a treatment with shock waves can produce a sensation of pain, potential skin redness and, under certain circumstances, hetatoma) but also the medication stress on the patient due to chemotherapeutic measures is reduced, or even eliminated (such chemotherapeutic measures sometime being required over a number of months). It is known to therapeutically treat certain kidney stone afflictions using focused shock waves, and efforts have also been made to treat gall stones by extracorporeal lithotripsy, as described in the article "Framentation of Gallstones By Extracorporeal Shock Waves," Sauerbruch et al., The New England Journal of Medicine, Mar. 27, 1986, pages 818-822. The nature and composition of gall stones, however, is different from that of kidney stones, and the effectiveness of known extracorporeal lithotripsy devices is not sufficient to destroy gall stones, using a number of shock waves which is acceptable to the patient's comfort, which results in disintegration of the gall stones to such an extent that the fragments can be naturally eliminated. Chemotherapeutic measures for partially or completely dissolving the fragments are therefore required. It is therefore a problem in the art to improve the effectiveness of extracorporeal lithotripsy devices to permit fragmentation of gall stones to an extent so that chemotherapeutic measures can be eliminated, or at least substantially reduced.
Experiments have also been undertaken in an effort to disintegrate urinary and biliary calculi using ultrasound energy as reported in "The Application of Ultrasound Energy to Urinary and Biliary Calculi," Coats, The Journal of Urology, Vol. 75, No. 5, May 1956, pages 865-874. Experiments were conducted in an effort to disintegrate gall stones in a laboratory simulation, the stones having been surgically removed from patients. The reported results stated that some additional (i.e., additional to the ultrasonic energy alone) physical force was required to disintegrate the calculi. Experiments were also reported in this article which were undertaken in an effort to disintegrate gall stones in living tissue. These experiments were unsuccessful, and the author concluded that ultrasonic treatment of calculi by the application of the energy source at the surface of the body seems impractical because, even with a focused crystal, the power required to penetrate from the surface to the calculus-containing organs, and to impress an adequate power dosage on the stone, would certainly be lethal to the intervening tissues and organs.
The application of ultrasound energy to accelerate human gall stone dissolution was reported in an abstract by Griffith et al. in The Journal of the Acoustical Society of America, Supplement 1, Vol 81, Spring 1987. It was reported that using a cholesterol stone solvent as the primary dissolving agent, dissolution of gall stones could be accelerated by the additional application of ultrasound energy.